Best way to query DynamoDB - amazon-web-services

Question

I'm trying to write a GraphQL server that queries an AWS DynamoDB store.
For the purpose of this question, the GraphQL part is irrelevant except for the fact that the arguments come in the form:
{
key1: value1,
key2: value2,
key3: value3
}
These key/value pairs are used to query against the database. Strict equality only, nothing fancy. All arguments are optional.
Here's what I came up with:
import { DynamoDB } from 'aws-sdk';
function constructParams(tableName, fields = {}) {
const keys = Object.keys(fields);
if (keys.length === 0) {
return {
TableName: tableName,
};
}
const filters = keys.map(key => `#${key} = :${key}`);
const attributeNames = keys.reduce((memo, key) => Object.assign(memo, {
[`#${key}`]: key,
}), {});
const attributeValues = keys.reduce((memo, key) => Object.assign(memo, {
[`:${key}`]: fields[key],
}), {});
return {
TableName: tableName,
FilterExpression: filters.join(' AND '),
ExpressionAttributeNames: attributeNames,
ExpressionAttributeValues: attributeValues,
};
}
function query(tableName, fields = {}) {
const docClient = new DynamoDB.DocumentClient({ region: 'ap-southeast-2' });
const params = constructParams(tableName, fields);
return new Promise((resolve, reject) => {
docClient.scan(params, (err, data) => {
if (err) {
reject(err);
} else {
resolve(data.Items);
}
});
});
}
export default query;
This works fine. But goodness it's cumbersome. My constructParams function feels like so much unnecessary boilerplate. Such a function would be completely unnecessary with MongoDB.
Put it this way, why does it feel like I'm writing SQL for a NoSQL database?

Answer 1

What you've written is indeed the shortest code possible for what you are trying to achieve, because that's how DynamoDB expects filtering information for a Scan.
You can also consider moving filtering from DynamoDB-side to client-side, if it helps decrease code complexity. This won't change the consumed read capacity units, so your read cost will remain the same.

Answer 2

Sadly, what I'm trying to achieve just isn't possible with DynamoDB.
The scan method superficially offers this functionality. But it really just returns the entire table set and then filters afterward. Once your data set reaches a certain size, scan ceases to work.
The query method is what you really should be using. But it won't permit queries on more than two keys. This is simply appalling. It is profoundly inadequate for a so called database.
In other words, the DynamoDB API isn't just syntactically primitive. It's also functionally primitive.